等间距法和均值标准差法界定城市热岛的对比研究

利用ASTER数据反演地表温度,采用等间距法和均值-标准差法,将研究区温度场分别划分为4级、5级、6级,并根据热岛区的界定进一步将4级、6级细分为4级(a)、4级(b)、6级(a)和6级(b)。在此基础上,对两种方法从城市热岛数量结构差异、热岛空间分布及细节表达等方面进行了系统对比分析。结果表明:两种方法所界定热岛的面积百分比随着分级数不同均出现跳跃现象,趋势基本一致。但就热岛强度而言,均值-标准差法对分级数的敏感性较等间距法小,在热岛的空间分布和温度变异的细节表现力等方面,均值-标准差法也优于等间距分级法。因此,综合来看,均值-标准差法是城市热岛界定的较适合方法。均值-标准差法以地表温度相对于平均温度的变异程度为依据进行热场划分,在多时相城市热岛演变、对比等研究中,一定程度上可以避开时相的差异。

Comparison Analyses of Equal Interval Method and Mean-standard Deviation Method Used to Delimitate Urban Heat Island

Fuzhou was chosen as our study area. Using Temperature/Emissivity separation algorithm, land surface temperatures （LST） were retrieved from ASTER （Advanced Spaceborne Thermal Emission and Reflectance Radiometer） data set which was collected on April 6th, 2004. Two methods named equal interval method and meanstandard deviation method were employed to divide land surface temperatures into four, five and six classes respectively. Synchronously, the domain of urban heat island （UHI） was determined according to its different definitions. Then multi-angle comparisons covering the structure, spatial distribution and the tiny undulation of the UHI delimitated by different methods were applied to choose the better methods. The result indicated that the percentage of the UHI area delimitated by both methods was fluctuant with the class number, while for the intensity of the UHI, mean-standard deviation method was less sensitive to the number of thermal field than that of equal interval method. Furthermore, the former was better than the latter in describing UHI spatial distribution and details. Based on standard deviation of land surface temperature against its mean value, the mean-standard deviation method, to some extent, likely minimized the problems that resulted from the inconsistent time periods of collecting remote sensing data in studying the multi-temporal urban heat island. However, our research was only a preliminary case study, more details and uncertainties about these methods and results needed to be further studied.